Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $115.96   7.839%   $125.0501   $125.05   $125.05   $125.10  
  Purchase #2 $55.41   5.438%   $58.4232   $58.42   $58.40   $58.40  
  Purchase #3 $69.33   7.544%   $74.5603   $74.56   $74.55   $74.60  
  Purchase #4 $102.94   6.244%   $109.3676   $109.37   $109.35   $109.40  
  Purchase #5 $198.27   9.477%   $217.06   $217.06   $217.05   $217.10  
  Purchase #6 $235.95   4.527%   $246.6315   $246.63   $246.65   $246.60  
  Purchase #7 $139.79   12.571%   $157.363   $157.36   $157.35   $157.40  
  7 purchase totals = $917.65       $988.4557   $988.45   $988.40   $988.60